Miniature device having an acoustic diaphragm

ABSTRACT

A method of forming a device having a compliant member includes creating a membrane having one or more elastomeric layers which are at least partially cured. Another elastomeric layer is provided on the membrane in an uncured state. At least one of a bobbin and a housing are positioned so that an end of the bobbin or housing, or the ends of both the bobbin and housing, extend at least partially into the uncured elastomeric layer. The uncured elastomeric layer is then cured to secure it to the membrane and to the housing or bobbin, or both the housing and bobbin. The method substantially reduces or eliminates the formation of holes that can form during fabrication or use of the device.

RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 15/182,069, filed Jun. 14, 2016 and titled “Miniature Device Havingan Acoustic Diaphragm,” the entirety of which application isincorporated by reference herein.

BACKGROUND

This disclosure relates to a miniature device having a compliant member.More particularly, the disclosure relates to a method of fabricating anacoustic diaphragm on the miniature device.

SUMMARY

In one aspect, a microspeaker device includes an acoustic diaphragm, ahousing, a bobbin and a coil. The acoustic diaphragm has a substantiallyplanar shape and includes a first layer of an elastomeric material and asecond layer of an elastomeric material disposed on the first layer ofelastomeric material. The housing has an end extending at leastpartially into the second layer, wherein the second layer adheres to thefirst layer and to a portion of the housing at the end of the housing.The bobbin has a surface and is disposed in the housing. The bobbin hasan end extending at least partially into the second layer, wherein thesecond layer adheres to a portion of the bobbin at the end of thebobbin. The coil is wound on the surface of the bobbin.

Examples may include one or more of the following:

The acoustic diaphragm may further include at least one intermediatelayer disposed between the first layer and the second layer. The atleast one intermediate layer may be formed of a viscous elastomericmaterial. The at least one intermediate layer may include a layer formedof an elastomeric material that is more viscous than the elastomericmaterial of the first layer and the elastomeric material of the secondlayer.

The first layer may have a thickness that is greater than a thickness ofthe second layer.

At least one of the first and second layers may be a silicone layer. Thesilicone layer may be formed of a room temperature vulcanizationsilicone.

An area of the acoustic diaphragm defined within a diameter of thebobbin may be stiffer than a surrounding annular area of the acousticdiaphragm.

The housing may be a tube having an opening at the end.

The elastomeric material of the first layer may be different from theelastomeric material of the second layer.

The second layer may include a meniscus formed at a surface of thebobbin or the housing.

The end of the housing may be in contact with a surface of the firstlayer and the end of the bobbin may be in contact with a surface of thefirst layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of examples of the present inventiveconcepts may be better understood by referring to the followingdescription in conjunction with the accompanying drawings, in which likenumerals indicate like structural elements and features in variousfigures. The drawings are not necessarily to scale, emphasis insteadbeing placed upon illustrating the principles of features andimplementations.

FIG. 1A, FIG. 1B and FIG. 1C are a perspective illustration, aperspective cutaway illustration and an exploded cutaway illustration,respectively, of an example of a microspeaker for a miniature earbud.

FIG. 2 is a flowchart representation of a method of forming a devicehaving a compliant member.

FIGS. 3A to 3E are cross-sectional illustrations showing sequentiallyhow the method of FIG. 2 is applied to fabricate a microspeaker device.

FIG. 4 is a magnified view of a portion of the end of the microspeakerdevice of FIG. 3D.

FIG. 5 shows a magnified cross-sectional view of a portion of analternative microspeaker device.

FIG. 6 shows an example of a microspeaker in which the intermediatelayer of the microspeaker of FIG. 5 is formed as three individuallayers.

DETAILED DESCRIPTION

Modern in-ear headphones, or earbuds, typically include microspeakers.The microspeaker may include a coil that is attached to an acousticdiaphragm either directly or through a bobbin on which the coil iswound. Motion of the diaphragm due to an electrical signal provided tothe coil results in generation of an acoustic signal that is responsiveto the electrical signal. The microspeaker typically includes a housing,such as a sleeve or tube, which encloses the bobbin, coil and a magneticstructure. As the size of the earbud decreases, it becomes increasinglydifficult to fabricate the acoustic diaphragm with an elastic suspensionat one end of the bobbin (or coil) and housing.

FIG. 1A, FIG. 1B and FIG. 1C are a perspective illustration, aperspective cutaway illustration and an exploded cutaway illustration,respectively, of an example of a microspeaker 10 that can be used in aminiature earbud. The microspeaker 10 includes a cylindrical housing 12having an opening at both ends. Inside the housing 12 is a bobbin 14that is nominally cylindrical in shape and which is open at least at oneend. The housing 12 and bobbin 14 are secured at one of their ends to acompliant member 16. In some examples, the housing 12 is made ofstainless steel and the bobbin 14 is made of a polyimide (e.g., KAPTON®)or polyethylene terephthalate (PET) (e.g., MYLAR®). A magnet assembly 18is secured to a platform 19 at an end of the housing that is opposite tothe compliant member 16. The magnet assembly 18 includes two magnetpieces 18A and 18B separated by a coin 18C. The magnet assembly 18extends along an axis 20 of the housing 12 and into an open regioninside the bobbin 14. In one example, the magnet pieces 18A and 18B arecylindrical neodymium magnets. A coil 22 is wound onto an outsidesurface of the bobbin 14. The bobbin 14 moves substantially along thehousing axis 20 in response to an electrical current conducted throughthe coil 22. In turn, a central circular portion of the compliant member16 moves axially and displaces air to thereby create an acoustic signal.

One technique for fabricating the compliant member 16 includes placingan open end of the housing 12 and an open end of the bobbin 14 into asingle thin layer of liquid silicone. The liquid silicone is then curedto form the compliant member 16. The central region of the compliantmember 16 that is located within the end region of the bobbin can bestiffened while the annular region that surrounds the central regionremains compliant. Difficulties arise with this technique as the liquidsilicone has a surface tension that causes the liquid to adhere to and“climb up” the walls of the housing 12 and the bobbin 14 to form ameniscus. The result is a reduction of the thickness of the cured layerof silicone which can lead to holes in the compliant member 16. Holescan form during the demolding process because the compliant member 16 isweak at thin areas. Thinned areas may result in holes or tearing beinggenerated during operation of the microspeaker.

FIG. 2 is a flowchart representation of an example of a method 100 offorming a device having a compliant member. Reference is also made toFIGS. 3A to 3E which are cross-sectional side view illustrationsshowing, in a sequential manner, the method 100 as applied tofabrication of a microspeaker device 20 in which the compliant member 16can subsequently be processed to form an acoustic diaphragm and asurround.

According to the method 100, a membrane is created (110) having one ormore elastomeric layers which are at least partially cured. As usedherein, the term “partially cured” means that a skin coat is formed ontop of an elastomeric layer to a degree that the elastomeric material inthat layer will not flow or mix with a new layer of liquid elastomericmaterial deposited on the partially cured layer. As an alternative, thedegree of cure can be controlled so that there is some mixing thatoccurs at the interface of two layers.

As shown in FIG. 3A, the membrane can be formed by depositing a layer 22of a liquid elastomeric material such as liquid silicone on a surface ofa substrate 24. The viscosity of the silicone generally is sufficientsuch that the thickness of the applied layer does not significantlychange although surface features and bumps typically disappear over timeuntil the surface is substantially flat. The liquid elastomeric materialis then partially or fully cured. In one example, the silicone is curedusing a platinum catalyst in a 150° C. environment for approximately 45minutes. Although not shown, this step may be repeated to form amulti-layer membrane by depositing one or more additional layers of aliquid elastomeric material and then partially or fully curing each ofthese layers before applying an additional layer. These subsequentlayers may be similarly cured at 150° C. but for longer times (e.g.,several hours or more). In alternative methods, an ultraviolet (UV) curemay be used or a room temperature vulcanization (RTV) silicone may beused.

The method 100 continues by providing (120) an uncured additionalelastomeric layer 26 on the layer 22 as shown in FIG. 3B. Referring toFIG. 3C, a housing 28 (only an end portion is shown) is positioned (130)such that the end of the housing 28 extends at least partially into theuncured elastomeric layer 26. In some instances, the housing 28 may bepositioned so that its end is in contact with the upper surface 29 ofthe layer 22 of the partially or fully cured elastomeric material. Astructure 30, such as a bobbin, (only an end portion is shown) ispositioned inside the housing 28 so that the end of the structure 30extends at least partially into the uncured elastomeric layer 26.Subsequently, the uncured elastomeric layer 26 is cured (140) so thatthe layer 26 is secured to the ends of the housing 28 and the bobbin 30,and adheres to the membrane 22. In one example, the housing 28 is in theform of a cylindrical tube and the bobbin 30 is configured to move in adirection along the tube axis.

After the final layer 26 is cured, the microspeaker device may beremoved from the substrate 24 as shown in FIG. 3D. The removal mayinclude a demolding process in which the compliant member (defined bythe combination of layers 22 and 26) is progressively released from thesubstrate 24, starting from the outside diameter of the device andprogressing toward the center. The portion of the compliant member 22and 26 that extends beyond the outer diameter of the housing 28 can betrimmed or removed by other means to limit the diameter to beapproximately equal to the outer diameter of the housing 28 as shown inFIG. 3E. When at rest, the compliant member formed according to themethod 100 has a substantially planar shape. The bobbin 30 and a coil(not shown) wound on the outer surface of the bobbin 30 are fullysupported by the compliant member, that is, the bobbin 30 is not incontact with any other structure. As described above, the central regionof the compliant member, i.e., the area defined within the diameter ofthe bobbin 30, can be stiffened to form the acoustic diaphragm while thesurrounding annular area defines a compliant surround that enables theacoustic diaphragm to moves axially and thereby generate an acousticsignal.

In some examples, the liquid elastomeric material used to form thelayers 22 and 26 is liquid silicone. Alternatively, one layer 22 can beformed from an elastomeric material that is different from theelastomeric material of the other layer 26 that is used to secure thehousing 28 and bobbin 30. In such implementations, the materials areselected for chemical compatibility to ensure good adherence between thelayers 22 and 26.

In the following example, the thickness of the layer 22 is greater thanthe thickness of the layer 26; however, in other implementations thethickness of the layer 22 may be the same as or less than that of thelayer 26. By way of a specific non-limiting numerical example, thethickness of the layer 22 may be 30 μm and the thickness of theadditional layer 26 may be 20 μm.

Referring to FIG. 4 which shows a magnified view of the end of thehousing 28 and the bobbin 30, the depth of the additional layer 26before curing may be chosen to achieve a liquid meniscus 36 formed atthe end of the housing 28 and another liquid meniscus 38 formed at theend of the bobbin 30 of desired sizes. Using a smaller thickness for theadditional layer 26 can limit the extent of the menisci 36 and 38 alongthe housing 28 and bobbin 30. In addition, thinning of the additionallayer 26 is less critical when the thickness of the underlying layer 22is substantially greater than the thickness of the additional layer 26.The extent of the menisci 36 and 38 along the housing 28 and the bobbin30 should be sufficient to enable support of the bobbin 30 and coilwhile affording proper adhesion to the underlying layer 22.

In some instances the bobbin suspended from the compliant member mayexhibit undesirable motion, such as rocking or other non-axial motion.To address this situation, the compliant member may be formed to providedamping, or dissipation, into the suspension. For example, the compliantmember may be formed of three layers as shown in FIG. 5. Specifically,two elastomeric silicone layers 40 and 42 may be formed with a low creepsilicone and an intermediate layer 44 formed with a more viscoussilicone gel. By way of a specific non-limiting example, the upper andlower layers 42 and 40 may be formed from a low creep silicone elastomersuch as ELASTOSIL® 3070/OO-20 SM and the intermediate layer 44 may beformed with POWERSIL® silicone gel available from Wacker Chemie AG ofMunich, Germany. Although the surround portion which is outside of theouter diameter of the bobbin 30 has increased loss in comparison to acompliant member without the viscous intermediate layer 44, thiscompliant member has the advantage of limiting the height of a resonancepeak and reducing unwanted rocking or sideways motion.

FIG. 6 shows an alternative example in which the intermediate layer 44is formed as three individual layers 44A, 44B and 44C. It should berecognized that any number of layers can be used to “build” theintermediate layer 44. A greater number of layers may be preferred whenusing lower viscosity elastomeric materials in an uncured state.

The examples described above provide advantages over a compliant memberformed from a single layer of an elastomeric material. The boundary atthe interface of the compliant member and the housing and/or otherstructure is better controlled. Generally there is less filleting andthinning of the member near the interface regions. Reduced thinningresults in a stronger device that is easier to demold from the flatsubstrate without tearing the compliant member. Moreover, the stiffnessof the suspension provided by the complaint member is more consistentlyachieved during manufacturing processes in comparison to a single layercompliant member.

A number of implementations have been described. Nevertheless, it willbe understood that the foregoing description is intended to illustrate,and not to limit, the scope of the inventive concepts which are definedby the scope of the claims. Other examples are within the scope of thefollowing claims.

What is claimed is:
 1. A microspeaker device comprising: an acousticdiaphragm having a substantially planar shape, the acoustic diaphragmcomprising: a first layer of an elastomeric material; and a second layerof an elastomeric material disposed on the first layer; a housing havingan end extending at least partially into the second layer, wherein thesecond layer adheres to the first layer and to a portion of the housingat the end of the housing; a bobbin having a surface and disposed in thehousing, the bobbin having an end extending at least partially into thesecond layer, wherein the second layer adheres to a portion of thebobbin at the end of the bobbin; and a coil wound on the surface of thebobbin.
 2. The microspeaker device of claim 1 wherein the acousticdiaphragm further comprises at least one intermediate layer disposedbetween the first layer and the second layer.
 3. The microspeaker deviceof claim 2 wherein the at least one intermediate layer is formed of aviscous elastomeric material.
 4. The microspeaker device of claim 3wherein the at least one intermediate layer comprises a layer formed ofan elastomeric material that is more viscous than the elastomericmaterial of the first layer and the elastomeric material of the secondlayer.
 5. The microspeaker device of claim 1 wherein the first layer hasa thickness that is greater than a thickness of the second layer.
 6. Themicrospeaker device of claim 1 wherein at least one of the first andsecond layers is a silicone layer.
 7. The microspeaker device of claim 6wherein the silicone layer is formed of a room temperature vulcanizationsilicone.
 8. The microspeaker device of claim 1 wherein an area of theacoustic diaphragm defined within a diameter of the bobbin is stifferthan a surrounding annular area of the acoustic diaphragm.
 9. Themicrospeaker device of claim 1 wherein the housing is a tube having anopening at the end.
 10. The microspeaker device of claim 1 wherein theelastomeric material of the first layer is different from theelastomeric material of the second layer.
 11. The microspeaker device ofclaim 1 wherein the second layer includes a meniscus formed at a surfaceof the bobbin or the housing.
 12. The microspeaker device of claim 1wherein the end of the housing is in contact with a surface of the firstlayer.
 13. The microspeaker device of claim 1 wherein the end of thebobbin is in contact with a surface of the first layer.